Frank r



(No Model.)

P. R. COLVIN. TELEPHONE SYSTEM.

Patented Jan. 7, 1896 AN DREW Ev GRAHAM FHOTMmm. WASH mmc N. M2.

UNITED STATES FFICB@ PATENT FRANK It. COLVIN, OF NEIV YORK, N. Y.,ASSIGNOR TO THE INTERIOR TELEPHONE COMPANY, OF SAME PLACE.

TELEPHONE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 552,823, dated January7, 1896. Application filed February 2, 1895. Serial No. 537,089. (Nomodel To @ZZ wiz/m, it may concern:

Beit known that I, FRANK R. CoLvTN, a citizen of the United States,residing in the city, county, and State of New York, have inventedcertain new and useful Improvements in Telephone Systems, of which thefollowing is a speciiication.

This invention relates to telephone systems, its object being to providea simple and effective central-oiice apparatus for coupling subscriberscircuits and permitting the central-office operator to hear and conversewith both connected subscribers without disturbing the relations oftheir circuits.

N'Vith this end in view I provide in each connecting-cord used to couplethe subscribers circuits an induction-coil, one winding of which is inseries with the cord and the other winding of which is in a localcircuit including a battery-transmitter, a battery and atelephone-receiver. 'With this provision the central operator may at alltimes hear and be heard by the subscribers without manipulating switchesas has heretofore been customary.

The novelty' of' the invention will be more fully explained hereinafterand will be definitely indicated in the claims.

In the accompanying drawing is diagraminatically shown a systemembodying my improvenients.

A B C represent three subscribers stations, the rst having a privateline connecting it with central oihce, and the other two having a commonline connecting them therewith.

The drawing illustrates a system equipped with metallic circuits, thoughthe main featuresof the invention may be carried out with groundedcircuits. At each station a magneto-bell l il lb is normally included incircuit, and switches 2 2, die., are provided for cutting it out andincluding a batterytransmitter 3 and receiver 4f. The switch is providedwith a hook to support the telephone and is so arranged that whenshifted to its talking position it will not support the telephone, thusinsuring a proper restoration of the circuits when conversation isconcluded. This construction is fully described and claimed in a patentgranted to me March 27, 1894i, No. 517,263.

In a normally-olsen ground at each station is a key 5 5, &c., by which abattery (i at central station may be thrown into circuit throughannunciators or indicators 7 7 in parallel relation to each other. Aconnectin g-cord or plurality of such cords is provided at central ohicebywvhich the several subscribers circuits may be interconnected. Thesecords, one pair of which is shown, terminate in switch-plugs S 9,comprising two metallic surfaces or cylinders insulated from one anotherand mounted on a common support. The inner cylinder is adapted` toengage a pin lO 10 of a jack-switch, and the outer one a springcontactll 1la of said switch. Thus when the two plugs are inserted in theVswitches corresponding to two subscribers circuits the subscribersA`instruments will be in circuit with one another. A battery l2 isinserted in that side of the cord which when the plug is in circuit willbe disconnected from the annunciator. In series relation With the otherside of each cord is one Winding of an induction-coil13, the otherwinding of which is in a local circuit la including a battery, carbontransmitter and receiver. The ratio of transformation of theinduction-coil is preferably 1:1. Each central operator is also providedwith a callingplug l5 connected or adapted to be connected with amagneto-call generator 1G and an answering-circuit including a battery,a transinitter and a receiver, as shown in circuit 17'.

Certain features of the system herein described are claimed in anotherapplication filed by me. The feature of novelty to which claim is madein the present application is the induction-coil 13 and its relation tothe connectingcord and listening circuit by which the central-officeoperator is in' continuous communicating relation to both subscribersduring transmission. As heretofore organized the listening-telephone isplaced in parallel relation to the talking-circuit, requiring a branchof very high resistance to prevent a diversion of too much current andreduction of the loudness of transmission at the distant stations.Obviously, with my organization, the induction-coil being in series maybe made of very low resistance and cannot divert any current from thedistant inlOO vio

struinents. The quality or ioudness of trimsl ,mission is Vthereforeunafieetcd amd is the' saine for all instruments in circuit. i Molte-Uover, the difference of resistance of two conznected circuits,:byvieasoncf diierenceof length or conductivityor 'different iocztlvatinospheific online conditions, cannot render vone instrument-feeble,as might be the cesse where the central-0fce iisteni11g-receiverisv in tbranch circuit across the line.

Having vthus described my invention, what v I cla-iin as new, and desireto secure by Letters v Patent, is-

1. rihecombination with :t number of tele-v v phone lines extending tothe cent1-ai station,

cfa cord connect-o1'foiiconnecting the cir cuits togetbeil forconversation, an induction coil having thesecondztry connected in serieswith v saidv cord vccnnectoi, and it telephone I transmitter andreceiver in circuit With the piininryof stid induction coil, Iwherebythe telephone set may remain continuously in op'-v erative connectionwith the coi-d connectorsubstantially asvdescribed. y

i?. A telephone system comprising t plurality of subscribers circuitsconnecting with t v central office, battery transmitters at the sev eralsubscribers stations, n eonnectingeord o1i cords stt central ofee, abattery for furnishingti-msnitting current :in circuit with' seid cord,and an induction vcoil having one winding; in series with the cord andthe other Winding vinn local listening circuit inciudin transmitting andreceiving' apparatus.

y In testimony whereof I have hereunto sul ,J

